The present invention relates to a display apparatus having a display panel in which display pixels are arranged in a matrix and a driving device for supplying to the display panel a gray scale voltage corresponding to display data. More specifically, the invention relates to a display apparatus that uses a liquid crystal material, organic EL, and plasma and its driving device for displaying.
JP-A-2001-13478 discloses a liquid crystal display apparatus source driver that constitutes a reference voltage generating circuit for generating a gamma correction reference voltage by resistive voltage division, and a resistance setting circuit for selecting a resistance to be used for the resistive voltage division from among a plurality of resistances. The reference further discloses that a gamma correction setting register receives data for setting the value of resistance, appeared on a display data line, in response to a clock signal CK when an enable signal E goes to “H”, and then switching on or off respective switches for resistances and other switches that comprise the reference voltage generating circuit according to the bit value of the received data for setting the value of resistance, thereby determining the reference voltage.
JP-A-6-348235 discloses a liquid crystal display apparatus that constitutes a liquid crystal display panel having a X signal line and a Y signal line, a horizontal driver for selecting a gray scale signal from among a plurality of gray scale signals supplied from a gray scale voltage generating circuit, on the basis of a data signal of an image to be displayed, for supply onto the X signal line of the liquid crystal display panel, and a vertical driver for supplying a liquid panel scanning signal onto the Y signal line of the liquid crystal display panel. The reference further discloses that the gray scale voltage generating circuit constitutes a plurality of fixed resistances interposed in series between the sides of the reference voltage of a high potential and the reference voltage of a low potential, and voltage varying unit for varying a voltage at a connection point between the fixed resistances to a voltage between the high potential reference voltage and the low potential reference voltage, thereby supplying the voltage at the connection point between the fixed resistances as a gray scale signal. The reference furthermore discloses that by adjusting the resistance value of a variable resistance in the above-mentioned manner, the voltage level of the gray scale signal or a gray scale voltage can be arbitrarily adjusted, so that gray scale characteristics can be freely modified.
JP-A-11-24037 discloses a gray scale voltage generating circuit that constitutes amplification unit for generating a variable intermediate-level gray scale voltage from an intermediate-level reference voltage and amplification unit for supplying gray scale voltages of negative polarity. The former amplification unit divides a reference supply voltage with the resistance divided for amplification, thereby generating a higher gray scale voltage of positive polarity and a lower gray scale voltage of positive polarity. Then, the amplification unit further divides these voltages with the resistance divided, thereby generating the intermediate-level reference voltage. Finally, the amplification unit generates the variable intermediate level-gray scale voltage from the intermediate-level reference voltage, using a variable resistance as a feedback resistance. The latter amplification unit inverse-amplifies all the gray scale voltages of positive polarity, obtained by dividing the resistive voltage and then amplifying the reference supply voltage, at the same amplification factor with respect to a liquid crystal GND potential, for supply as the gray scale voltages of negative polarity. The reference further discloses that the gray scale characteristics can be adjusted just by adjusting a single variable resistance.
In the above-mentioned art, however, among 64 gray scale levels of voltages, the voltages at the two ends are fixed as a GND voltage or the reference voltage externally supplied. Accordingly, adjustment to the gray scale voltage fixed as the GND voltage is impossible. Further, for adjustment to the gray scale voltage fixed as the reference voltage, an additional adjustment circuit becomes necessary outside the gray scale voltage generating circuit, thus leading to an increase in the number of components. Though there are some cases where adjustment to the voltages of the gray scale levels at the two ends becomes necessary due to the characteristic differences of liquid crystal display panels, the above-mentioned techniques did not take such cases into consideration.
JP-A-11-175027 discloses a liquid crystal driving circuit that constitutes a latch address control circuit, a first holding circuit, a second holding circuit, setting registers, a gray scale voltage generating circuit, a gray scale voltage selector circuit, and an amplifier circuit. The latch address control circuit sequentially generates latch signals that receive display data. The first holding circuit holds the number of display data equivalent to the number of output data lines in response to a latch signal, and the second holding circuit receives and then holds the number of display data held in the first holding circuit, equivalent to the number of the output data lines in response to a horizontal synchronization signal. The setting registers control the value of a gray scale voltage. The gray scale voltage generating circuit receives a plurality of different reference voltages to generate a gray scale voltage specified by one of the setting registers. The gray scale voltage selector circuit selects a gray scale voltage according to the display data held in the second holding circuit, and the amplifier circuit shifts the gray scale voltage selected by the selector circuit so as to be more closer to an offset voltage, and amplifies the gray scale voltage by an amplitude factor specified by one of the setting registers, for supply. The reference further discloses that the setting registers for setting the amplification factor of respective operational amplifiers in the amplifier circuit are provided for respective R, G, and B display colors, and that a voltage setting can be changed according to each of the colors. The reference further discloses that an offset voltage setting can be changed, because the offset voltage of the amplifier circuit is generated by dividing an offset reference voltage with the resistance divided and a common voltage, using a plurality of variable resistances, the resistance value of which can be set. In the above-mentioned art, however, an offset adjustment circuit becomes necessary in the amplified circuit. Thus the size of the driving circuit becomes large, so that the cost of the circuit increases. Further, in this art, a gamma correction control register sets the resistance values of all the variable resistances in a resistance ladder for adjustment so as to obtain a desired gamma characteristic. Accordingly, if the resistance value of a single variable resistance is adjusted, the overall resistive voltage division ratio would be changed. This leads to a change in all the gray scale voltages. Thus, in order to adjust gray scale voltages according to the respective characteristics completely, it would take much time. Further, The reference does not disclose adjustment to the gray scale voltage amplitude.
JP-A-2001-22325 discloses a liquid crystal display apparatus that constitutes a pair of amplifiers, a voltage dividing circuit for generating a plurality of a pair of symmetrical reference voltages of positive and negative polarities from standard voltages of positive and negative polarities, and a variable voltage generating circuit for supplying a pair of symmetrical reference voltages of positive and negative polarities for gray scale adjustment to a pair of voltage dividing points in the voltage dividing circuit, associated with specific intermediate gray scale levels. The reference further discloses that by increasing a positive reference voltage Vx−2 from a positive reference voltage Vx−1 by a desired value and decreasing a negative Vx+1 from Vx by the desired value simultaneously in the variable voltage generating circuit in a normally white mode, the voltage values of reference voltages V0 to Vx−2, Vx+1 to V2x−1 can be changed smoothly. The reference discloses that, with this arrangement, adjustment to and modification of a gray scale level-brightness characteristic can be easily performed by a single variable voltage generating circuit.
However, the above-mentioned art does not display insertion of a variable resistance into the reference voltage generating circuit, and does not disclose adjustment to the amplitude of a gray scale voltage.